1. Technical Field
The present disclosure relates to a technique of estimating an uncomfortable sound pressure by using electroencephalogram.
2. Description of the Related Art
Hypacusia means difficulty in hearing sounds of a specific frequency or a frequency band, for example. The frequency or frequency band which presents hearing difficulty differs from user to user.
A hearing aid amplifies sounds so that the user can hear the sounds. The necessary amount of amplification differs for each user because auditory characteristics are different from user to user.
Prior to beginning use of a hearing aid, fitting is conducted to determine a gain for each sound frequency. In order to perform fitting, it is necessary to accurately measure the auditory characteristics of a user.
In an auditory characteristics test, a hearing threshold level (HTL) is determined first. Next, an uncomfortable level (UCL) is determined. The HTL and the UCL are used for determining a dynamic range of sound pressure for sounds to be output from a hearing aid.
Methods of measuring UCL by using electroencephalogram are being developed.
For example, the document of Thornton, A. R., Yardley, L., & Farrell, G. (1987), “The objective estimation of loudness discomfort level using auditory brainstem evoked responses. Scandinavian Audiology, 16, 219-225” (referred to as “Document 1” hereinafter) discloses that there is correlation between a V wave latency of an auditory brainstem response (ABR) to a click sound and the UCL.
The document of Zenker-Castro, F., & Barajas de Prat, J. J. (2008), Auditory steady-state responses and hearing device fitting Part A: The role of auditory steady-state responses in fitting hearing aids. (pp. 241-258). In G. Rance (Ed.), The auditory steady-state response: Generation, recording, and clinical application. San Diego: Plural, (referred to as “Document 2” hereinafter) discloses that, from the amplitude of an auditory steady state response (ASSR) to an amplitude-modulation sound, the loudness felt by the person can be approximated. With the technique described in Document 2, frequency-by-frequency UCL estimation is impossible, and the estimation requires 30 minutes or more, and the accuracy of estimation may be low for loud sounds that are near the UCL.